A known apparatus for controlling a pump driving motor is disclosed in JP2002-506406A (corresponding to U.S. Pat. No. 6,719,377). According to the apparatus disclosed, a drive pattern of the motor (i.e., motor drive pattern) constituted by a voltage threshold value and a duration time is determined. The voltage threshold value is compared with a voltage that the motor generates when a power supply to the motor is in an OFF state, i.e., a voltage that the motor serving as a generator generates from an induced electromotive force (which will be hereinafter simply referred to as a “generation voltage”). The duration time is a time period during which the power supply to the motor is retained in an ON state.
The power supply to the motor is ON/OFF controlled by the motor drive pattern so that the power supply is switched from the OFF state to the ON state when the generation voltage generated by the motor falls to or below the voltage threshold value while the power supply to the motor is in the OFF state, and the power supply is switched from the ON state to the OFF state after the power supply is retained in the ON state for the duration time. Accordingly, an average rotational speed of the motor (and therefore an average fluid volume discharged from a hydraulic pump) can be controlled to be greater when the voltage threshold value is larger and the duration time is longer during the anti-skid control. The fluid volume discharged from the hydraulic pump, in this case, is the volume of fluid discharged from the hydraulic pump per time unit.
In the cases where the rotational speed of the motor is low during the anti-skid control, the fluid volume discharged from the hydraulic pump (i.e., fluid discharge volume of the hydraulic pump) becomes small, which may cause a reservoir to be filled with a brake fluid. In this case, an issue such as a stroke of a brake pedal that increases, and a wheel cylinder pressure that is prevented from sufficiently decreasing during a pressure-reducing control of the anti-skid control, may be raised. On the other hand, when the rotational speed of the motor is high, an issue such as an operating noise of the motor and the hydraulic pump that increase, may be raised. That is, during the anti-skid control, it is considered that the rotational speed of the motor is desirably specified to be low when the volume of brake fluid in the reservoir (i.e., reservoir fluid volume) is small while the rotational speed is specified to be high when the reservoir fluid volume is large.
In addition, since a master cylinder pressure (and therefore a discharge pressure of the hydraulic pump) acts as a load of the hydraulic pump, the rotational speed of the motor becomes low when the master cylinder pressure is large in the cases where the motor drive pattern is fixed.
Accordingly, as disclosed in JPH09-267736A, JP2001-505505A (corresponding to U.S. Pat. No. 6,339,738), and JP2005-59627A, it is known that the reservoir fluid volume and the master cylinder pressure are estimated, and then the motor drive pattern is selected in such a way that in which an average power supply to the motor is larger (i.e., precisely, the voltage threshold value is larger or the duration time is longer) when the estimated reservoir fluid volume (i.e., reservoir fluid estimated value) is larger or the estimated master cylinder pressure (i.e., master cylinder pressure estimated value) is larger.
As a result, regardless of the reservoir fluid volume or the master cylinder pressure, the rotational speed of the motor (and thus the fluid discharge volume of the hydraulic pump) can be specified to be an appropriate value. The motor drive pattern determined on the basis of the reservoir fluid estimated value and the master cylinder pressure estimated value will be hereinafter referred to as a “motor base drive pattern”.
Even if the motor drive pattern is fixed, the rotational speed of the motor may become small (and thus the fluid discharge volume of the hydraulic pump may become small) along with a progress of a deterioration of the motor. In addition, even if the rotational speed of the motor is fixed, the fluid discharge volume of the hydraulic pump may become small along with a progress of a deterioration of the hydraulic pump. Further, in the cases where the reservoir fluid estimated value or the master cylinder pressure estimated value is calculated to be smaller than an actual value, the motor base drive pattern in which the average power supply to the motor is smaller may be selected, which may cause a lower rotational speed of the motor (and thus a smaller fluid discharge volume of the hydraulic pump).
That is, in the cases where the motor or the hydraulic pump becomes deteriorated, or the reservoir fluid estimated value or the master cylinder pressure estimated value is calculated to be smaller than the actual value, an insufficiency of the fluid discharge volume of the hydraulic pump may occur when the motor is driven by the motor base drive pattern. As a result, an issue such as a stroke of a brake pedal that increases, and the wheel cylinder pressure that is prevented from sufficiently decreasing in the pressure-reducing control of the anti-skid control, may be raised.
On the other hand, in the cases where the reservoir fluid estimated value is calculated to be larger than the actual value, the motor base drive pattern in which the average power supply to the motor is larger is selected. Thus, the rotational speed of the motor becomes high when the motor is driven by the motor base drive pattern. An issue such as an operating noise of the motor and the hydraulic pump that increase, may be raised
Thus, a need exists for an apparatus for controlling a pump driving motor that can securely select an appropriate motor drive pattern and retain a rotational speed of the motor at an appropriate level.